An engine may misfire for a variety of reasons including a concentration of exhaust gas within a cylinder being greater than desired, an air-fuel mixture within a cylinder being too lean, and/or spark energy being less than desired. One way to determine whether or not a cylinder of an engine has misfired is by monitoring engine acceleration and deceleration. If the engine does not accelerate after a cylinder passes top dead center of its compression stroke and before a subsequent cylinder in the engine firing order passes top dead center of its compression stroke, it may be determined that an engine cylinder has misfired. However, it may be difficult to distinguish engine acceleration from combustion in a first cylinder from engine acceleration from combustion in a second cylinder at higher engine speeds because engine combustion events are spaced close in time. Consequently, it may not be possible to take misfire mitigating actions for the one cylinder that is exhibiting misfire without adjusting operating conditions of all cylinders. Therefore, cylinders that are adjusted and not misfiring may be operated less efficiently than is desired.
The inventor herein has recognized the above-mentioned disadvantages and has developed a method for operating an engine, comprising: opening and closing an exhaust valve of a cylinder during a cylinder cycle; and beginning sampling an exhaust pressure sensor in an exhaust passage of the cylinder after opening the exhaust valve during the cylinder cycle and ending sampling at or before closing the exhaust valve during the cylinder cycle; and adjusting operation of the cylinder in response to sampling the exhaust pressure sensor.
By sampling exhaust pressure of a cylinder only during exhaust valve opening of the cylinder, it may be possible to determine engine misfire in cylinders that are misfiring without indicating misfire in a cylinder that is not misfiring. Further, a peak pressure of an exhaust pressure pulse from a cylinder relative to average exhaust pressure may provide a higher signal to noise ratio than engine acceleration relative to an average engine speed. Consequently, an exhaust pressure based engine misfire detection system may provide fewer false positive indications of misfire.
The present description may provide several advantages. For example, the approach may provide improved engine misfire detection at higher engine speeds. Additionally, the approach may eliminate sources of noise, such as cylinder blow through, from exhaust pressure data so that a higher confidence in cylinder misfire may be provided. Further, the approach may provide for improved misfire control for individual cylinders.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.